1. Field of the Invention
The present invention relates to a method for manufacturing a fluid bearing with two bearings, such as a thrust bearing and a radial bearing, and to a fluid bearing manufactured by the method.
2. Description of Related Art
FIG. 11 shows an example of a conventional fluid bearing. As shown in the figure, a shaft 1 with grooves la for generating radial dynamic pressure is inserted into an inner hole of a bearing 2. The bottom end of the shaft 1 is press-fitted in a thrust plate 4 that is provided with thrust dynamic pressure bearing grooves 4a and 4b at its top and bottom surfaces. The thrust plate 4 is interposed between a counter plate 5 situated under the shaft 1 and the bearing 2. The counter plate 5 is fixed to the bearing 2 with an adhesive to seal the bearing 2 to complete a bearing assembly.
A radial dynamic pressure bearing 3 is formed between the shaft 1 and the bearing 2, and the dynamic pressure bearing works to support the shaft 1, in a manner that the shaft 1 is freely rotatable. Thrust dynamic pressure bearings 4a and 4b are formed between the thrust plate 4 that is press-fitted at the bottom end of the shaft 1 and the counter plate 5 placed at the opening on the bottom end of the bearing 2 and functioning as a lid to seal the bottom end of the bearing 2, and between the thrust plate 4 and the side of the bearing 2 facing the thrust plate 4. The thrust dynamic pressure bearings support the thrust load.
In this way, the conventional fluid bearing functionally separates the thrust bearing and the radial bearing and is structured to have these separate functions with separate parts. Furthermore, the two bearings are manufactured using different machining methods. For example, radial bearings are manufactured by cutting or rolling machining, whereas thrust bearings are manufactured by press machining, edging machining or electrolytic machining.
As a result, in a conventional fluid bearing such as the one described above, separate structures for the radial bearing and the thrust bearing make it difficult to obtain a highly accurate perpendicularity between the radial and thrust bearings; and the lack of perpendicularity have an impact on the performance of the motor itself.
Furthermore, because the radial bearing and the thrust bearing have separate structures, it is difficult to maintain optimal spaces both between the shaft and the radial bearing and between the shaft and the thrust bearing. This consequently makes it difficult to maintain a balance between the radial force and the thrust force.
Moreover, the conventional fluid bearing is likely to lack in press-fit strength between the thrust plate 4 and the shaft 1. On the other hand, when the press-fit strength is increased, problems such as stress fatigue and destruction likely occur.
In addition, the separate structures for radial and thrust bearings result in a large number of parts, and numerous process steps in the assembly that require high precision, such as press-fitting the shaft 1 and the like, which cause increased cost.
The present invention has been made to solve the problems described above existing in prior arts. It is an object of the present invention to provide method for manufacturing a fluid bearing in which two sets of bearing grooves, i.e., thrust bearing grooves and radial bearing grooves, are integrally formed to have a unitary structure, which achieves a high roundness and a high perpendicularity, and has few parts to allow cost reduction. It is also an object of the present invention to provide fluid bearings manufactured by the method.
In accordance with one embodiment of the present invention, a method for manufacturing a fluid bearing includes the steps of inserting a fluid bearing manufacturing tool into a hole created in a work piece and flowing a electrolytic solution between the manufacturing tool and the work piece, wherein a power source for electrolytic machining is connected between the manufacturing tool and work piece, and forming grooves for fluid bearing on an inner surface of the work piece through electrolytic machining. In one aspect of the embodiment, a mask member having at least two sets of grooves provided at least two places along an axial direction is fixed on the outer surface of an electrode section of the manufacturing tool to which the power source for electrolytic machining is connected. Each of the groove sets consists of multiple grooves in a shape corresponding to the fluid bearing grooves. An electrolytic solution is allowed to flow into the grooves on the mask member to simultaneously form fluid bearing grooves at two places along the axial direction on the inner surface of the work piece facing the respective groove sets.
As a result, the fluid bearing grooves can be simultaneously formed at at least two places, and more preferably, at two places, through electrolytic machining on the inner surface of the work piece facing each of the groove sets provided in the mask member. Accordingly, at least two radial bearings or a thrust bearing and a radial bearing can be formed in a unitary structure, which allows the manufacture of fluid bearings with superior perpendicularity and greatly improved quality.
Moreover, because the grooves are formed by electrolytic machining, burrs that may occur in mechanical machining are not created on the work piece, and metal chips within the grooves will be dissolved and discharged such that metal-burning by metal chips does not occur. As a result, the quality can be significantly stabilized.
In accordance with the embodiment, an electrolytic solution pathway may preferably be formed inside the electrode section of the manufacturing tool to allow the electrolytic solution to branch out and flow to the groove sets at two places on the mask member along the axial direction. The mask member adhere closely to the inner circumferential surface of the work piece, such that the electrolytic solution flows only to the grooves on the mask member, in order to form fluid bearing grooves on the inner surface of the work piece facing the groove sets.
By having the mask member closely adhere to the inner surface of the work piece and by having the electrolytic solution flow only to the grooves on the mask member to perform electrolytic machining, the machining time is shortened to 5xcx9c10 seconds, a large number of grooves can be readily formed, and the machining cost can be reduced.
In accordance with one embodiment of the present invention, the electrode section of the manufacturing tool is provided with at least two groove forming surfaces, and more preferably at two places, along the axial direction where the mask member is attached. The groove forming surfaces form an angle xcex8 with respect to the axial direction, where the angle xcex8 is 0xc2x0xe2x89xa6xcex8xe2x89xa690xc2x0. In a preferred embodiment, one of the groove forming surfaces of the manufacturing tool extends in the axial direction, and the other of the groove forming surfaces is angled at an angle xcex8 with respect to the axial direction, where the angle xcex8 is 0xc2x0xe2x89xa6xcex8xe2x89xa690xc2x0.
As a result, two sets of grooves for two radial bearings or a set of grooves for a radial bearing and a set of grooves for a thrust bearing at a specified angle with respect to the radial bearing set of grooves can be formed simultaneously.
In accordance with one embodiment of the present invention, a method for manufacturing a fluid bearing includes the steps of inserting a work piece into a hole created in a fluid bearing manufacturing tool and flowing a electrolytic solution between the manufacturing tool and the work piece, wherein a power source for electrolytic machining is connected between the manufacturing tool and work piece, and forming grooves for fluid bearing on an outer surface of the work piece through electrolytic machining. In one aspect of the embodiment, a mask member having at least two sets of grooves provided at least two places along an axial direction is fixed on the inner surface of an electrode section of the manufacturing tool to which the power source for electrolytic machining is connected. Each of the groove sets consists of multiple grooves in a shape corresponding to the fluid bearing grooves. An electrolytic solution is flown into the grooves on the mask member to simultaneously form fluid bearing grooves at two places along the axial direction on the outer surface of the work piece facing the respective groove sets.
In accordance with the embodiment, a mask member with a set of grooves, the set consisting of multiple grooves in a shape corresponding to the fluid bearing grooves at at least two places along the direction of the shaft, is fixed on the inner surface of the electrode section of the manufacturing tool to which the power source for electrolytic machining is connected. An electrolytic solution is flown into the grooves on the mask member, to simultaneously form fluid bearing grooves at two places along an axial direction of the work piece on the outer surface of the work piece facing the respective groove sets. As a result, two radial bearings or a thrust bearing and a radial bearing can be integrally formed as a unitary structure, which would result in superior perpendicularity, greatly improved quality and significantly improved motor performance.
In addition, because the grooves are formed by electrolytic machining, burrs that may occur in mechanical machining are not created on the work piece, and metal chips within the grooves will be dissolved and discharged such that metal-burning by metal chips does not occur. As a result, the quality can be significantly stabilized.
In this invention, by having an electrolytic solution pathway formed inside the electrode section of the manufacturing tool to allow the electrolytic solution to branch out and flow to groove sets at two places on the mask member along the direction of the shaft and by having the mask member adhere closely to the outer surface of the work piece, the machining time can be shortened and numerous grooves can be readily formed, thereby reducing the machining cost.
In accordance with another embodiment of the present invention, a fluid bearing has a bearing and a rotary shaft rotatably supported by the bearing, in which at least two groove sets of to generate dynamic pressure are formed on the inner surface of the bearing and/or on the outer surface of the rotary shaft at two places along an axial direction of the rotary shaft. Each of the groove sets consists of multiple grooves. Lubrication fluid is allowed in the grooves to generate dynamic pressure by the relative rotation between the rotary shaft and the bearing. The two groove sets form an angle xcex8 against the axial direction of the rotary shaft, where the angle xcex8 is in the range 0xc2x0xe2x89xa6xcex8xe2x89xa690xc2x0, and each of the grooves has a rectangular cross-sectional shape formed by electrolytic machining.
In a preferred embodiment, one of the groove sets extends in the axial direction of the rotary shaft, and the other groove set extends at an angle xcex8 with respect to the axial direction of the rotary shaft wherein the angle xcex8 in the range 0xc2x0xe2x89xa6xcex890xc2x0.
In accordance with the present invention, the groove sets consisting of multiple grooves are located at two places along the axial direction of the rotary shaft and the two groove sets form an angle xcex8, where the angle xcex8 is in the range of 0xc2x0xe2x89xa6xcex8xe2x89xa690xc2x0, and the cross-sectional shape of each of the grooves is rectangular. As a result, a fluid bearing with different sets of bearings, such as, for example, two radial bearings, a set of thrust and radial bearings or the like, can be readily manufactured by changing the angle xcex8 (0xc2x0xcx9c90xc2x0).
Other features and advantages of the invention will be apparent from the following detailed description, taken in conjunction with the accompanying drawings that illustrate, by way of example, various features of embodiments of the invention.